1. Field of the Invention
The present invention relates generally to fluid seals for establishing a seal between a shaft and a housing which are rotatable relative to one another and, more particularly, to so-called unitized oil seals. In particular, the present invention is concerned with a novel unitized seal structure having an improved dirt exclusion capability and wherein a good oil sealing action is accomplished without recourse to the use of a conventional garter spring.
2. Description of the Prior Art
The unitized oil seals have been used advantageously in motor vehicles and related applications. As disclosed, for example, in U.S. Pat. No. 4,448,426 to Jackowski et al, U.S. Pat. No. 4,531,748 to Jackowski, U.S. Pat. No. 5,004,248 to Messenger et al, and U.S. Pat. No. 5,269,536 to Matsushima et al, a unitized oil seal includes a wear sleeve element and a seal element which are coupled together to form a single unitized assembly. In use, the wear sleeve element is press fit over a shaft such as a fixed or rotary axle of the vehicle and the seal element is press fit within a counterbore of a housing such as a wheel hub.
When the sealing lips of the seal element or the wear surface of the wear sleeve are worn out, the unitized seal may be replaced as a whole with a new one. The benefit of the unitized seal is that the outer surface of the axle is free from wear so that the life of the axle is increased.
As illustrated in the patents cited above, a unitized oil seal generally includes a so-called dust lip or dirt exclusion lip serving to prevent ingress of dust and dirt. The function of the dust lip is important in protecting the primary sealing lip from a premature wear.
In applications such as heavy trucks, it is often encountered that the unitized seals are used throughout an excessively long distance drive before the wheels are overhauled for replacement of the seals. In these situations, it is desirable that the dust lips properly sustain their intended function throughout the life of the unitized seals.
It is therefore an object of the present invention to provide a unitized oil seal having a high degree of dirt exclusion capability.
Another problem associated with the conventional unitized seals is related to the provision of a garter spring. For the purposes of ready reference, the seal structure illustrated in U.S. Pat. No. 5,269,536 to Matsushima et al is reproduced in FIG. 1 of the accompanying drawings. As shown therein, the conventional unitized seal design generally employs a garter spring 1 to bias a primary sealing lip 2 into sealing engagement with the wear sleeve element 3. The garter spring is snap fit within a spring groove 4 formed on the circumferential periphery of the primary sealing lip.
To install a new unitized seal, it is the general practice to first press fit the unitized seal within a counterbore 5 of the wheel hub 6 in the direction shown by the arrow F in FIG. 1 and to then mount the wheel hub onto the axle 7. As a rule, the operator is recommended to use a hydraulic or mechanical press so as to press fit the unitized seal without shock into the hub. However, where such a press is not available, the operator in some instances may use an impact tool such as a hammer to drive the seal into the hub. The impact of hammering may occasionally cause the garter spring to slip out of the spring groove. If after installation the operator overlooks to inspect the garter spring to see whether it is properly positioned, there is a risk that the garter spring is inadvertently lost. This would result in an insufficient sealing pressure of the primary sealing lip and, hence, would lead to a leakage of lubricant.
Accordingly, another object of the present invention is to provide a unitized oil seal wherein a conventional garter spring is eliminated and which is yet capable of providing an adequate oil sealing function.